This invention relates generally to a system for measuring line spaces on a curved surface and particularly to a system for measuring the line width, space width, and period of a black matrix on a kinescope faceplate.
During the production of picture tubes for color television receivers, a black matrix is applied to the inside surface of the faceplate panels. The black matrix consists of parallel lines which extend vertically as defined by the viewing orientation of the tube. Black lines are spaced at desired intervals leaving transparent glass in the spaces between the matrix lines. The transparent spaces are coated with slurries of materials containing phosphors which emit the three primary colors of light red, green and blue when impacted by electrons. The three phosphors are alternately applied in a repetitive sequence such as red, green and blue to all the transparent spaces of the panel. Prior to the application of the phosphors, it is desirable to measure the barwidths formed by the transparent spaces and the opaque matrix lines to verify that they are within acceptable dimensional tolerances in order to avoid the expensive application of phosphors to improperly matrixed faceplates.
In order to measure the line widths and space widths of each barwidth, the faceplate panel is placed between a stationary light source and a detector. Light is passed through the spaces within the matrix to the light detector. A portion of the panel is scanned with light in a direction substantially perpendicular to the matrix lines and the variation in light caused by the opaque lines and the transparent spaces is detected by the detector and provided to a measuring system. The panel is moved to various positions and the scanning and measuring repeated. The panel surface which carries the matrix is curved and accordingly linear motion of the faceplate would cause the distance from the light source to the matrix lines to vary and the projection of the matrix lines on the detecting elements within the detector would also vary. For this reason, the relative motion of the panel and the light source is accomplished utilizing a device which maintains a curved surface a constant distance from a stationary point as the surface moves relative to the point. A device which accomplishes such motion is described in application Ser. No. 466,594 entitled "Device for Maintaining a Moving Curved Surface a Constant Distance from a Stationary Point" filed on even date herewith by Larry S. Gullman, the disclosure of which is incorporated by reference herein.
The verification of the acceptability of the matrix requires investigation of four matrix characteristics. Three color phosphors are used in producing a color television picture, and accordingly every fourth transparent space receives the same color producing phosphor. For this reason as the spaces are measured, an unacceptable space must be associated with a particular color to assist in correcting the processing step which caused the unacceptability. Additionally, the widths of the transparent spaces must be measured to assure that the proper amount of each phosphor can be applied. Also, the widths of the opaque lines must be measured to assure that the matrix lines are not visible to the viewer. Finally, the period of the matrix pattern must be measured to assure that the proper ratio of phosphor and black matrix can be applied to the panel. The instant invention is directed a system which fulfills these requirements.